The present invention relates to a method for conditioning gas containing entrained asphaltene-containing hydrocarbons for pipeline transportation, and a method for preparation of a surface active compound for use in such conditioning.
It is well known that gas and liquid oil products are preferably separated prior to their transportation through respective gas and oil pipelines. To this end, hydrocarbons produced from subterranean wells are regularly processed through crude-gas separation units prior to introduction to their respective transportation lines. Under some conditions, these crude-gas separation units allow liquid hydrocarbons to remain entrained within the separated gas. If the entrained crude oil contains asphaltene, the asphaltene and other entrained hydrocarbons combined with the agitation and other conditions supplied by the flow of gas combine to form an emulsion which adheres to the walls of the gas lines. Changing conditions in the gas lines result in a breaking of the adhering emulsion. Water evaporates leaving deposits of porous asphaltene on the interior surfaces of the gas lines, which themselves create obstructions in the gas lines, and which additionally act as a sieve to catch particles of other material thereby exacerbating the blockage problem.
The emulsions are formed by gradual cooling of the gas as it advances through the gas line after leaving the crude-gas separator. Condensation of water vapor and also fractions of hydrocarbons having 3 to 7 carbon atoms integrate with entrained petroleum dispersed in fine particles within the gas stream, as well as the entrained asphaltene and any inorganic material which may be present. Natural agitation caused by the flow of the fluid provides the necessary energy for formation of the emulsions, which are found to possess a high viscosity, frequently more than 60,000 centipoise, and a high capacity of adherence to the walls of the pipes. These emulsions typically have a composition by weight of 60-70% sweet water, 6-13% petroleum, 10% asphaltenes, up to 20% condensate, and up to 1% inorganic matter.
The conditions which bring about the presence of the emulsion forming products in the gas stream are various, but may include situations as follows. Hydrocarbons are occasionally produced from wells at rates which are higher than can be efficiently handled by crude-gas separating stations. If it is not feasible to also increase the capacity of the separating station, liquid hydrocarbons which may contain asphaltenes will remain in the stream of gas. Also, periods of maintenance or repair of the separation station may require hydrocarbons to be produced without the desired level of separation prior to introduction of the gas to the gas line. In these circumstances, when the flow rate is reduced or the separator is placed back on line, so that the entrainment of oil in the gas line diminishes or ceases altogether, the greater concentration of condensate in the emulsion causes the deposition of asphaltene in the gas lines, and a breaking of the emulsion, thus liberating the water. The asphaltenes deposited in the gas line adhere to the pipe as a solid porous deposit capable of entrapping inorganic particles flowing in the gas stream, resulting in restrictions in the flow area within the pipe and, in critical cases, total obstruction of the gas transportation line.
Removal of these solid deposits is accomplished with various known mechanical equipment, such as pipe scraping tools or "pipe pigs". The use of these mechanical devices requires the gas line to be temporarily shut down while the mechanical scraping of the interior of the pipes is carried out. The scraping devices also frequently produce stresses in excess of the design specifications of the pipes being cleaned. Finally, periods during which the gas line is out of action due to scraping result in wastage of the gas and condensate normally passed through the transportation lines, which must be burned during the cleaning operation. Further, the scraping operations produce solid waste materials which must then be disposed of.
It is therefore a principal object of the present invention to provide a method whereby formation of asphaltene deposits can be avoided by adding an active chemical formulation to fluids so as to inhibit emulsion formation.
It is a further object of the present invention to disclose a method for preparation of a surface-active compound for treatment of the stream of gas to achieve the above principal objects.
Other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following summary and detailed description of the invention.